Collie Eye Anomaly (CEA) is a canine hereditary ocular disorder affecting development of the choroid and sclera. The disease segregates in several dog breeds including Rough and Smooth Collies, Border Collies, Australian Shepherds, Lancashire Heelers, and Shetland Sheepdogs. The clinical phenotype varies significantly among affected dogs of all breeds. The primary CEA phenotype, choroidal hypoplasia (CH), is characterized by regional hypoplasia (underdevelopment) of the choroid, which is the highly vascularized bed of the eye that underlies the retina. This lesion usually results in an opthalmoscopically detectable window defect in the ocular fundus located temporal to the optic nerve.
In the most mildly affected dogs, CH is the only lesion apparent, and many such dogs will exhibit no obvious clinical consequences and retain apparently normal vision throughout life. In severely affected dogs, there may also be colobomatous lesions of the optic nerve head and or adjacent tissues. Colobomas are outpouchings of the eye wall, where there is localized thinness of the sclera. In the most severe cases, localized or complete retinal detachments, and/or intraocular neovascularization and hemmorrhage can develop, all of which can lead to blindness. These severe manifestations of CEA are only seen in dogs also affected with the primary choroidal hypoplastic lesion.
It has been previously established (Lowe J K, et al. Genomics 2003 July; 82(1):86-95) that the primary CEA phenotype is inherited via a gene that maps to a 3.9-cM region of canine chromosome 37, and segregates as an autosomal recessive trait with nearly 100% penetrance. However, because there has been no identification of an alteration of the gene associated with CEA, screening for the disease has not been possible. Thus, there has been an ongoing need in the canine breeding industry for a genetic test that permits direct identification of dogs that are normal, carriers or affected with CEA.